The PON technology is a broadband optical access technology most widely applied at present. The conventional PON system includes an optical line terminal (OLT), a passive optical splitter, an optical network unit (ONU), a trunk fiber, and the like. The trunk fiber, the optical splitter, and a branch fiber between the OLT and the ONU are together called an optical distribution network (ODN). In the uplink direction, the ONU transmits uplink data in a burst mode and the OLT receives the uplink data in the burst mode. In the downlink direction, the OLT transmits downlink data in a continuous mode, and the ONU receives the downlink data in the continuous mode.
The conventional PON system covers a small range, so that a great number of OLTs are required to expand the coverage. Therefore, a solution of implementing LR-PON by using regenerator remote connection in an electrical relay manner is proposed in the prior art.
FIG. 1 illustrates basic architecture of a system for implementing LR-PON by using an optical-electrical-optical (OEO) relay device. A reamplifying, reshaping, retiming (3R) relay device is disposed between the optical splitter and the OLT to serve as a remote connection relay device between the OLT and the ONU for accomplishing reamplifying, reshaping, and retiming functions. The 3R device receives an uplink burst packet transmitted by the ONU in a burst manner, and transmits the uplink burst packet with aligned phases to the OLT in a “burst transmission” manner. Further, with the increase of the distance, a plurality of 3R relay devices may be disposed between the optical splitter and the OLT.
Because the 3R relay device transmits uplink data in the “burst transmission” mode, a receiving device has to receive the uplink data forwarded by the 3R relay device in a “burst reception” mode.
During the implementation of the present invention, the inventor finds that the prior art at least has the following problems.
The cost for the receiving device adopting the “burst reception” mode is high, which leads to the problem that the cost for establishing an LR-PON system is too high.